The present invention relates to a wet image forming method and apparatus applied to, e.g., an electrophotographing apparatus or electrostatic recording apparatus to form an image using a liquid developer.
A wet image forming apparatus using a liquid developer comprising toner particles and solvent can use very fine toner particles on the submicron order, which cannot be used in a dry image forming apparatus. Thus, it can realize high image quality.
Toner particles comprise resin and pigment. Dry-type toner particles have a higher ratio of pigment to resin, than dry-type toner particles. This apparatus is economical since a sufficiently high image density can be obtained with a small amount of toner.
Wet image forming apparatuses and methods are disclosed in, e.g. U.S. Pat. Nos. 5,255,058, 5,276,492, 5,028,964, 5,636,349, 4,728,983, 5,061,583, and 5,570,173.
A conventional wet image forming apparatus has several problems, and one of them is degradation in image quality of a transfer image.
Conventionally, since a toner image attached to the photosensitive body is directly transferred to a sheet with an electric field, transfer non-uniformity occurs due to variations in electric field corresponding to the unevenness on the surface of the sheet. This results in degradation of image quality.
In addition, defective transfer tends to occur due to variations in the environment, e.g. temperatures and humidity at the location of use of the image forming apparatus, or in the electric characteristics of the sheet.
Solutions to these problems are disclosed, for instance, in U.S. Pat. Nos. 5,148,222, 5,166,734 and 5,208,637. In the apparatus disclosed therein, a toner image is once transferred from the photosensitive body to an intermediate transfer medium, and then the image is transferred from the intermediate transfer medium to a recording medium such as paper, using pressure or pressure and heat.
It is relatively easy to form the intermediate transfer medium of a material having surface smoothness and less variation in electric resistance. Thus, compared to the case of directly transferring the toner image onto paper with an electric field, the degradation in image quality of the transfer image can greatly be improved.
Moreover, the solvent in the toner image attached to the intermediate transfer medium can be evaporated by heat or sucked away by air before the toner image is transferred to the sheet. Thus, the amount of solvent attached to the paper can be reduced.
Jpn. Pat. Appln. KOKOKU Publication No. 46-41679, Jpn. Pat. Appln. KOKAI Publication No. 62-280882, etc. disclose apparatuses that do not employ electric field transfer but employs transfer by pressure or transfer by pressure and heat in both the transfer of the toner image from the photosensitive body to the intermediate transfer medium and the transfer from the intermediate transfer medium to the paper.
However, even if the toner image is transferred to the paper by pressure or by pressure and heat, as mentioned above, the occurrence of toner remaining after transfer cannot completely be prevented, and satisfactory transfer efficiency cannot be obtained.
The present invention has been made in view of the situations described above, and its object is to provide an image forming method and image forming apparatus in which a developer image is transferred with a shearing stress, thus enhancing the transfer efficiency of the developer image.
According to an aspect of the present invention, there is provided an image forming method comprising: forming an electrostatic latent image on a surface of an electrostatic latent image carrying body; supplying a developer on the electrostatic latent image, and developing the electrostatic latent image into a developer image; and transferring the developer image from the electrostatic latent image carrying body to a recording medium, while applying a shearing stress to the developer image.
According to another aspect of the invention, there is provided an image forming apparatus comprising: a latent image forming device which forms an electrostatic latent image on a surface of an electrostatic latent image carrying body; a developing device which supplies a liquid developer on the electrostatic latent image formed by the latent image forming device, and develops the electrostatic latent image into a developer image; a condensing device which condenses the developer image; and a transfer device which transfers the developer image condensed by the condensing device to a recording medium, while applying a shearing stress to the developer image.
According to still another aspect of the invention, there is provided an image forming apparatus comprising: a latent image forming device which forms an electrostatic latent image on a surface of an electrostatic latent image carrying body; a developing device which supplies a liquid developer on the electrostatic latent image formed by the latent image forming device, and develops the electrostatic latent image into a developer image; a transfer device which transfers the developer image developed by the developing device from the electrostatic latent image carrying body to an intermediate transfer medium, and then transfers the developer image from the intermediate transfer medium to a recording medium; and a condensing device which condenses the developer image transferred on the intermediate transfer medium, wherein a shearing stress is applied to the developer image during at least one of a time of transferring the developer image from the electrostatic latent image carrying body to the intermediate transfer medium and a time of transferring the developer image from the intermediate transfer medium to the recording medium.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.